This invention relates to containers whose body walls are comprised of a layer of very thin metallic material. More particularly, this invention relates to body curls at the marginal end portions of such containers and to the art to hermetically securing metal end closures to such curled containers for packaging pressurized products therein.
Presently, there is a desire among can manufacturers to reduce the overall cost of manufacturing containers especially those used for packaging pressurized products such as beer and carbonated beverages. There have been at least two main approaches to cost reduction. One has been to further reduce the body wall thicknesses of already thin highly-directional highly-worked containers such as aluminum and steel drawn and ironed containers, for example, for aluminum, from about 0.008 at the open marginal end portion and about 0.006 inch therebelow, to less than about 0.0057 inch overall, and for steel, from about 0.0068 inch at the open marginal end portion and about 0.0045 inch therebelow, to less than about 0.004 inch overall. The other approach has been to substitute the aforementioned thin highly-worked metal containers with less costly composite ones whose body walls include a fibrous layer and an inner layer of full hard metal foil whose temper is about H19 and whose thickness is about 0.001 inch.
Both of these approaches have heretofore been unsuccessful because, in securing metal end closures to drawn and ironed aluminum container body walls less than about 0.0083 inch, drawn and ironed steel container body walls less than about 0.0053 inch thick, and composite container body walls whose foil liners are less than about 0.002 inch thick, hermetic seals or seams resistant to product internal pressures could not be obtained. The reason in each case is that conventional double seaming methods have been used. These require forming a conventional flange of the marginal end portion of the container body walls. But conventional 0.090-0.100 inch flanges cannot be formed of the marginal end portions of such thin highly-directional highly-worked metal containers, because the wall metal there will not elongate to the extent required. It is too thin, too brittle, and elongation during flanging occurs in the same axial grain direction created in the drawing and ironing process. This inability to elongate as required produces cracks in the flanges and such flanges preclude obtaining hermetic pressure resistant seams such as double seams.
Flanges cannot be used on composite container bodies because the thin hard foil liner likewise often cracks due to elongation during flanging.
Heretofore, can manufacturers have sought to overcome flange cracking and resulting inhermetic seams by necking-in or providing extra metal in certain end regions of can body walls for example by beefing up the thickness of the metal there by about 0.002 inch or more and by use of sealant materials in double seams. Neither remedy prevents cracks in flanges and each remedy is costly and brings on its own problems. For example, providing extra metal at end regions of drawn and ironed bodies makes it difficult to strip them from their drawing punches.
Even if uncracked flanges satisfactory for seaming could be obtained in these thin highly-worked container bodies, flanges in such bodies would be less than desirable because they are sharp and can cause damage to sealing rubber gaskets of can testing and can filling machines. Also, flanged thin highly-worked metal container bodies are usually weak at their upper regions and are highly susceptible to denting, crushing and other abuse during storage and handling.
It has now been found that by employing a body curl instead of a flange, the aforementioned flange-related problems are reduced and hermetic seams resistant to product internal pressures can be obtained. Body curls have been found to require less metal elongation than conventional flanges. Whereas the latter requires 7-8% elongation, the former requires less than about 4% elongation. Because of this, body curls formed of extremely thin highly-worked metal containers rarely have cracks or puckers, and any cracks which might be formed in the foil liner of the composite fibrous container body curl are so slight that they do not interfere with the formation of hermetic pressure resistant seams.
It has also been found that hermetic pressure-resistant seams between metal end closures and containers for pressurized products such as beer and carbonated beverages, can be formed by a mechanical interference between, and the substantially axial compressive force exerted by, the end portion of the end closure coverhook and the compressed marginal end portion of the container body curl. A thermoplastic adhesive that need not require heat activation, placed between the vertical end closure countersink wall and the metal container body wall, assists in making the seam pressure resistant. The adhesive also protects the edge of the body wall from contact with the packaged product.
The aforementioned compressive interference seam saves metal because the metal end closure flange need not be as long as a conventional one for double seaming. This seam is also advantageous because it can be formed with only minor adjustments to conventional double seaming equipment.
In view of the above shortcomings of flanging, and of the above and other advantages of curling the marginal end portions of the aforementioned very thin metal walled container bodies, as well as of seaming them to metal end closures by a substantially axial compressive interference seam, it is an object of this invention to provide an open-ended cylindrical metallic container body whose wall comprises metal whose thickness adjacent its open end is less than about 0.0057 inch and whose marginal end portion is in the form of a body curl capable of forming hermetic pressure-resistant seams with metal end closures.
Another object of this invention is to provide very thin highly-worked drawn and ironed containers for beer and carbonated beverages wherein the container body wall has a uniform thickness of less than 0.0057 inch.
Another object of this invention is to provide the aforementioned container wherein the uniform thickness for drawn and ironed aluminum containers is about 0.0053 inch and for drawn and ironed steel containers is about 0.0038 inch thick.
Another object of this invention is to provide an open-ended cylindrical metallic drawn and ironed container body capable of holding internal pressures of from 60-90 psi at elevated temperatures of up to around 130.degree. and 140.degree. F, whose body wall is comprised of metal whose thickness at its marginal end portion is less than 0.0057 inch, is in the form of a body curl whose edge points toward the container body wall and which is capable of forming a hermetic pressure-resistant seam.
Another object is to provide an open-ended composite cylindrical container body whose full hard metal foil liner is less than about 0.002 inch thick and whose marginal open end portion includes a body curl.
Another object of this invention is to provide a method of hermetically and pressure resistantly securing a metal end closure to a container body whose body wall comprises metal whose thickness is less than 0.0057 inch.
Another object of this invention is to provide the aforementioned method wherein the container body wall is comprised of extremely thin highly-worked drawn and ironed and like metallic materials.
Another object of this invention is to provide the aforementioned method wherein the container body wall is comprised of a layer of fibrous material and an inner layer of full hard metal foil whose thickness is less than about 0.002 inch.
Another object of this invention is to provide a hermetic pressure-resistant seam between a metallic end closure and a container body whose wall adjacent its marginal end portion is in the form of a body curl and which comprises a layer of metallic material whose thickness is less than 0.0057 inch.
Still another object of this invention is to provide the aforementioned seam wherein the seam is effected by the mechanical interference between and the substantially axial compressive force exerted by the metal end closure hook and the body curl.
Still another object of this invention is to provide a thin-walled container for beer and carbonated beverages having a seam of the aforementioned type.
Yet another object of this invention is to provide a sealed thin-walled container of the aforementioned type wherein the thickness of the container body wall is uniform.
These and other objects and advantages of this invention will be apparent as it is better understood from the description which follows, which taken in conjunction with the drawing discloses preferred embodiments thereof.